It is common for round balers to have an expandable bale forming chamber between opposing vertical sidewalls. Cooperating transverse chamber walls are defined by a continuous apron and/or a plurality of rolls. Frequently the apron consists of an array of side-by-side belts trained around a series of rollers for either guiding or driving the apron. During field operation, crop material such as hay is picked up from the ground and continuously fed into the expandable chamber where it is rolled into a compact cylindrical package, wrapped with twine, net or the like and subsequently ejected onto the ground. During chamber expansion the apron belts move outwardly as the girth of the bale increases. Belt tension provides resistance against such outward movement and thereby is determinative of bale density.
Balers of the type mentioned above employ various systems for tensioning the apron during bale formation. For example, one successful arrangement is disclosed in U.S. Pat. No. 4,425,753, issued Jan. 17, 1984 in the name of John H. Freimuth, wherein a round baler having a bale forming chamber defined by sidewalls, an apron and a floor roll utilizes a pair of tension spring sets. Each set consists of four coil springs arranged in a diamond shaped pattern operatively mounted on one or the other of the sides of the baler frame to exert force on the apron assembly.
Other prior art round balers have used hydraulic systems in the tensioning systems. Illustrative of this is U.S. Pat. No. 4,698,955, issued Oct. 13, 1987 in the name of Robert A. Wagstaff, which discloses an expandable chamber round baler in which single acting hydraulic cylinders maintain force on a pivotal chamber wall comprising a plurality of rollers.
Air spring assemblies have also been used in prior art baler systems for maintaining a predetermined amount of tension on the apron during bale formation to control the density, as shown in U.S. Pat. No. 4,748,801, issued Jun. 7, 1988 in the name of Ronald T. Sheehan, et al.
In another known prior art technique, springs and hydraulic cylinders are used in combination for apron tensioning, as taught in U. S. Pat. Nos. 4,391,187, issued Jul. 5, 1983 in the name of Richard W. Koning, et al, and 4,899,651, issued Feb. 13, 1990 in the name of H. Nevin Lausch. In these systems a pair of springs and a pair of hydraulic cylinders are separately connected between the baler sides and an apron take up mechanism that moves as the girth of the bale being formed increases.
Although prior art round baler apron tensioning systems have met with varying degrees of success, there is always a need for a less complicated and inexpensive system that enhances the overall operation of round balers by improving performance and reliability of the machine.